Mutations in the LRRK2/Dardarin gene are a common cause of autosomal dominant Parkinson's disease (PD). Several dominantly inherited missense mutations have been identified in a number of families that exhibit a broad spectrum of neuropathological features, including deposition of alpha-synuclein and tau proteins. LRRK2 (leucine-rich repeat kinase 2) encodes a large, multifunctional protein. It belongs to the ROCO protein family and includes a protein kinase domain of the MAPKKK class and several other major functional domains including Ras/GTPase and WD40 domains. It is difficult at this juncture to fully appreciate how mutations in the LRRK2 gene cause PD, as its function is largely unknown. We propose to generate and characterize LRRK2 knockout mice to gain a better understanding of LRRK2 function and to determine whether the absence of LRRK2 function is the cause of PD due to LRRK2 mutations. We plan to utilize the recent technological advances in the generation of inhibitor sensitizing mutations to introduce a mutation into the LRRK2 kinase domain that will allow the specific inhibition of the LRRK2 signaling cascade. Introduction of the drug in drinking water or by injection will permit the specific and reversible inhibition of LRRK2 kinase activity at any time during development or aging. Such an innovative approach provides an extremely valuable method to dissect the role of LRRK2 signaling in PD. Moreover, it will enable a molecular dissection of the role of LRRK2 kinase activity in maintaining a functional nigrostriatal dopamine system during development, early postnatal development and within the mature and diseased brain. Our targeting strategy will also enable us to create a null mutation in LRRK2 as well as tissue specific deletion of LRRK2 using the Cre-Lox system. Accordingly experiments are proposed to further characterize the role of LRRK2 in the pathogenesis of PD. In Specific Aim #1 we will develop and characterize a reversible and temporally inducible LRRK2 knockout mouse using a novel method of reversible and temporally specific interruption of kinase activity in cells and animals. In Specific Aim #2 we will we will evaluate the sensitivity of LRRK2 gene targeted mice to environmental toxins including MPTP-induced dopaminergic cell death. In Specific Aim #3 we will determine whether LRRK.2, a-synuclein and/or tau participate in a common pathogenic pathway by crossing LRRK2 gene-targeted mice with a-synuclein and tau transgenic mice. Development and characterization of a reversible and temporally inducible LRRK2 knockout mouse, will increase our understanding of the relationship of LRRK2 kinase activity in the pathogenesis of PD. Moreover, it may provide insight into the molecular mechanisms by which mutations in this gene induce neuronal damage and may provide novel therapeutics targets to prevent the toxic effects of this familial associated gene in the degenerative process of PD. [unreadable] [unreadable]